The art of kinetic spray coating, or cold gas dynamic spray coating, is discussed at length in an article by T. H. Van Steenkiste et al., entitled "Kinetic Spray Coatings", published in Surface and Coatings Technology, Vol. 111, pages 62-71, on Jan. 10, 1999. Extensive background and reference to prior patents and publications is given as well as the current state of the art in this field as summarized by the thirteen listed authors of the referenced article.
The work reported on was conducted with an apparatus developed for the National Center for Manufacturing Services (NCMS) which improved upon the prior work and apparatus reported in U.S. Pat. No. 5,302,414 Alkhimov et al., issued Apr. 12, 1994. These sources have reported the kinetic spray coating of metals and other materials by gas accelerated impact on certain substrates with varying degrees of success using a high pressure kinetic spray system with a kinetic spray nozzle based upon concepts taught by Alkhimov et al. and other sources.
The method involves feeding metallic or other material types in the form of small particles or powder into a high pressure gas flow stream, preferably air, which is then passed through a de Laval type nozzle for acceleration of the gas stream to supersonic flow velocities greater than 1000 m/s and coated on the substrate by impingement on its surface. While useful coatings have been made by the methods and apparatus described in the referenced article and in the prior art, the successful application of these methods has been limited to the use of very small particles in a range of from about 1 to 50 microns in size. The production and handling of such small particles requires special equipment for maintaining the smaller powder sizes in enclosed areas and out of the surrounding atmosphere in which workers or other individuals may be located.
Accordingly, the ability to utilize a kinetic spray coating process for coating metal and other particles larger than 50 microns would provide significant benefits.